1. Field of the Invention
The present invention relates to a back light module adopted for use in a dual-sided display, and more particularly, to a back light module having a simplified structure.
2. Description of the Prior Art
With the development of liquid crystal display (LCD) technologies, LCD display panels have been widely applied to various consumer electronic products such as digital cameras, personal digital assistants, mobile phones, and flat TVs. A back light module, a key component in an LCD display, is installed in the back side of an LCD display panel for providing the LCD display panel with light.
The back light module substantially includes a plurality of cold cathode fluorescent lamps (CCFL) arranged in parallel, and a combination of various optical components such as diffusion plates and prisms for providing the LCD display panel with a brilliant and even light source. Cold cathode fluorescent lamps have to be driven by a high AC voltage, and moreover, they have to be respectively driven by different inverters. If an inverter is used to drive a plurality of cold cathode fluorescent lamps, the ballast of the inverter cannot be maintained stable, which results in an uneven brightness of the cold cathode fluorescent lamps. As a result, each cold cathode fluorescent lamp requires independent conducting wires to connect to an inverter, and this limitation increases the difficulty in allocating internal components and in housing design of the LCD. For a single panel LCD, the inverters and the conducting wires can be hidden under the reflecting plate or the rear frame of the back light module without influencing the illumination of the back light module.
However, for a dual-sided display, the allocation of the inverters and the conducting wires becomes a problem to be solved. The dual-sided display is composed of two parallel LCD display panels, and a back light module installed in between the LCD display panels. Therefore the back light module has to be open on both sides and a reflecting plate is not allowed. In such a case, the inverters and the conducting wires cannot be arranged under the reflecting plate, and have to be installed somewhere inside the back light module without influencing the illumination of the back light module. Generally, the conducting wires are positioned in the peripheral region of the display, nevertheless, this region is originally designed for other components, such as driving circuits of the display. In addition, since each cold cathode fluorescent lamp requires an inverter, the allocation of the internal components for the dual-sided display becomes more difficult.
Please refer to FIG. 1 and FIG. 2. FIG. 1 is a top view of a conventional back light module 10 for use in a dual-sided display, and FIG. 2 is a cross-sectional view of the back light module 10 shown in FIG. 1. As shown in FIG. 1 and FIG. 2, the back light module 10 is positioned between parallel LCD display panels 20 for providing a light source for both of the LCD display panels 20. The back light module 10 includes a frame 12, and a plurality of cold cathode fluorescent lamps 14 (CCFL) fixed in the frame 12. Each cold cathode fluorescent lamp 14 includes two electrodes 14A and 14B exposed outside the frame 12. In addition, the back light module 10 further includes a plurality of inverters 16 corresponding to the cold cathode fluorescent lamps 14 for converting DC voltage into AC voltage. Each inverter 16 has two conducting wires 16A and 16B respectively connected to the electrodes 14A and 14B so as to provide the cold cathode fluorescent lamps 14 with proper driving voltages. Furthermore, the back light module 10 usually includes two diffusion plates 18, each positioned between the cold cathode fluorescent lamps 14 and the respective LCD display panel 20 for scattering the light beams irradiated by the cold cathode fluorescent lamps 14.
As described, for the conventional back light module 10, the same amount of inverters 16 as cold cathode fluorescent lamps 14 has to be installed to provide corresponding driving voltages. This increase in inverters means an increase in cost. Besides, redesigns for extra space for allocating the inverters 16 and the conducting wires 16A and 16B conflict with dimensional requirements of a small size display. In addition, the inverters 16 are high frequency components, and therefore an increase in the amount of inverters 16 generates increased electromagnetic interference.
Therefore, any reduction in quantity of inverters for a dual-sided display would result in a more flexible design and effectively economize cost.